By-pass circuit for electromagnetic rectifiers



Dec. 18, 1956 F, KESSELRlNG l-:TAL 2,774,933

BY-PASS CIRCUIT FOR ELECTROMAGNETIC RECTIFIERS Filed Jan. l5, 1955 2 Sheets-Sheet 1 Anw/e N575 Dec. 18, 1956 F. KEssELRlNG ET AL 2,774,933

BY-PASS CIRCUIT FOR ELECTROMAGNETIC RECTIFIERS Filed Jan. 13, 1955 2 Sheets-Sheet 2 BY MM g United States Patent() BY-PASS CIRCUIT FOR ELECTROMAGNETIC RECTIFIERS Fritz Kesselring, Zollikon Zurich, and Ernst Egli, Aarau,

Switzerland, assignors to FKG Fritz Kesselring Garatebau, A. G., Bachtobel-Weinfelden, Switzerland, a' corporation of Switzerland Application January 13, 1955, Serial No. 481,678

8 Claims. (Cl. 321-48) Our invention relates to electromagnetic rectiers and is more particularly directed to a by-pass circuit to allow the electromagnetic switch contacts to close on zero voltage.

Electromagnetic rectifiers, of the type to which our novel invention applies, have an electromagnetic structure which operates a substantially massless electromagnetic armature into and out of engagement with a stationary contact. A commutating reactor, which is a saturable type reactor, is provided in series with the cooperating contacts to limit the contact current for a small interval of time to its magnetizing current during the make and break interval of the contacts. An auxiliary circuit or so called by-pass circuit is then provided to initiate contact closure by means of an auxiliary closing coil on the electromagnetic switch magnetic structure.

It is well known that electrical contacts, operating under the influence of instantaneous voltage are subject to rapid deterioration due to small arcs immediately before contact engagement. These small arcs cause pitting, and the initial pitting then leads to more serious pitting until the accumulative process causes complete deterioration of the contact. Since electromagnetic rectifier contacts operate 216,000 times per hour when rectifying a sixty cycle source, the problem of contact deterioration is particularly severe. it is therefore extremely desirable to close the contacts on zero voltage.

In the past, electromagnetic rectitiers have had by-pass circuits whereby the initiation of current in the by-pass circuit ilows through a closing coil of the electromagnetic switch in order to close the switch contacts. Current is initiated through this by-pass circuit in phase with the potential applied to the rectifier phase in question. Because of this, instantaneous voltage across the contacts when the contacts nally engage can be very high. This type of rectier then achieves voltage regulation by delaying the initiation oi' current through the by-pass circuit, and the instantaneous voltage on the contacts is varied, depending on the magnitude of regulation.

Electromagnetic rectiers of this type are described in copending applications Serial No. 416,843 iiled March 17, 1954, and Serial No. 257,398, filed November 20, 1951, both assigned to the assignee of this application.

A by-pass circuit for an electromagnetic rectifier using the same above mentioned principle, hence having instantaneous voltage across the contacts during the Amake process, is also shown in Patent No. 2,619,628, issued November 25, 1952.

rille principle of our invention is to supply an auxiliary voltage in the by-pass circuit phase shifted from the voltage that will fall across the contacts during the make in such a way that the by-pass circuit will initiate contact closure when the contact voltage is Zero.

Voltage control is then achieved by means of a flux reversal circuit such as is shown in copendin-g application 2,774,933 Patented Dec. 18, 1956 ing the electromagnetic switch contacts at a point where the instantaneous voltage on the switch contacts is always zero, we now vary the length of the commutating reactor make step, thus varying the output voltage to the load.

It lis therefore a primary object of our invention to supply an electromagnetic rectier in which the instantaneous voltage across the contacts at the make is zero.

Another object of our invention is to provide an electromagnetic rectifier in which the make voltage is approximately zero regardless of output voltage regulation.

A further object of our invention is to provide an electromagnetic rectier in which the make voltage across the contacts is independent of load current.

Still another object of our invention is an electromagnetic rectifier circuit in which the load current can be regulated continuously from no load to full load.

Another object of our invention is to provide an auxiliary voltage in a by-pass circuit which leads the secondary voltage so that the contact will close on zero voltage.

A still further object of our invention is to provide a by-pass circuit which carries current continuously in one direction.

Further objects of our invention will be apparent on consideration of the following description in connection with the drawings in which:

Figure l shows one embodiment of our invention.

Figure 2 shows the voltage-current-tirne relationships for the embodiment of Figure 1.

Figure 3 shows a second embodiment of our invention.

Figure 4 shows the voltage-current-time relationships for the circuit of Figure 3.

Figure l shows a three phase electromagnetic rectifier having a delta connected primary 21 supplying a Y-connected secondary 22. The choice of this type connection is arbitrary since my novel circuit has universal application. Each phase of the transformer secondary 22 has `in series a commutating reactor 28, an electromagnetic switch 24, a swinging choke 30, and a load 29. The commutating reactor 28 has a ux reversal winding 33. For purposes of simplification, the complete ux reversal circuit is not shown but it can be of the type shown in copending application Serial No. 423,358, tiled April 15, 1954.

The electromagnetic switch 24 shown in Figure 1 has an opening means 51, a holding or main winding 25, a closing Winding 26, and a biasing winding 27. The opening means 51 shown in Figure l is shown as a spring bias. It should be noted, however, that this could oe an electromagnetic type opening means as disclosed in copending application Serial No. 416,843, led March 17, 1954, assigned to the assignee of the instant invention. The movable contact of electromagnetic switch 24 is shown as armature 50.

The biasing windings 27 are supplied from an outside source shown as D. C. source 31. The energy supplying source 31 could be taken from the primary winding of the main transformer 21 or the secondary transformer 22. This bias is merely used to obtain faster operation of contact 24.

Our invention is directed to the by-pass circuit for each phase, shown as the auxiliary voltage source 23, dry cell rectifier 32, closing winding 26 and back to the common point of Y-connected secondary 22.

The operation of Figure 1 is now explained in conjuncltion with the voltage-current-timey relationship shown in FigureZ.

It will be assumed that the armature 50 in phase marked V3 for secondary winding 22 is closed and the armature 50 in the phase marked V1 is about to close. For this case, Figure 2 shows the phase voltages V1 and V3.

Since the voltage which will appear across armature i) when it closes will be the difference between voltage V1 and V3, armature 5t) will close on a zero voltage if closed at time t1 in Figure 2, that is, at the time when V1 equals V3. In order to accomplish contact closure at t1, the by-pass circuit consisting of auxiliary winding 23, diode 32, and closing winding 26, must be initiated at the point shown at to in Figure 2. That is, the auxiliary voltage in phase V1 must lag the voltage V3 by a predetermined angle.

The current under these conditions through the closing coil 26 is shown in Figure 2 as i1. Since this current is initiated at to, at tr the number of ampere turns required to close armature 5t) will be reached in closing winding 26. Hence armature 50 will now close on zero voltage.

Upon closure of armature 50, a circuit is provided for the main current flow through commutating reactor 28, contact 59, swinging choke 30, and load 29. However, commutating reactor 2S will present an almost infinitely high empedance for a given length of time (make step) to the current attempting to flow. Hence a step is provided to protect contact Si! against inrush current.

The length of the make step given by the commutating reactor, which is in turn adjusted by the value of the flux reversal circuit 33, now determines the output voltage to load 29. The above mentioned make step is shown in Figure 2 as the time between t1 and t2. At t2, the commutating reactor saturates and the main current shown as l1, flows through the closed armature 50 and load 29.

Since the auxiliary voltage is phase shifted from the main voltage, the by-pass current i1, decreases to zero, before the main current decreases to zero, at time t3. The main current subsequently decreases but the armature 59 is held closed because of the ampere turns in holding coil 25. At t4 the current becomes low enough for the commutating reactor to unsaturate, and the current is maintained at a very small value. Since this low current is not high enough to suiiiciently energize holding coil 25, the contact opens at l5.

Note that the by-pass current of the circuit shown in Figure 1 is independent of the magnitude of load current or voltage regulation. Hence the exact time of contact closure, that is, the point shown as t1 in Figure 2 can be accurately adjusted regardless of operating conditions. This operation is achieved by providing the proper phase shift for auxiliary winding 23, and providing the by-pass circuit with an impedance to give the current the correct rate of rise.

Figure 3 presents a second embodiment of my novel circuit for an electromagnetic rectifier. The components of this ligure are numbered exactly as those of Figure l.

This circuit utilizes the same principle of providing an auxiliary voltage which is phase shifted from the main voltage in order to get contact closure at zero voltage. However, this circuit will supply a range of load current from zero current to rated current. Note that in the circuit of Figure l the by-pass circuit current by-passes the load and merely forms a closed circuit returning to the common point of the Y connected secondary. Hence load current will flow only when the by-pass current is high enough to operate the cooperating contacts.

In the circuit of Figure 3, the by-pass circuit current is in series with the load. Therefore, the by-pass current will flow to the load even though it is below the operative value of the electromagnetic switch. However, the rate of rise of by-pass current will be slightly dependent upon load impedance. The voltage-current-time relationship For the circuit of Figure 3 is shown in Figure 4.

Figure 4 shows the by-pass current z' as a solid line for the case of high impedance load and as a dotted line i for the case of a low impedance load. Note that because of the varying load impedance, the magnitude and rate of rise of by-pass current changes. Accordingly, the required value of ampere turns in closing coil 26 is reached at a different time depending upon load impedance. in Figure 4, contact closure is shown at time t1 for a high impedance load and time t1' for a low impedance load.

This means that the contact will not close exactly under zero voltage for all conditions. However, as shown in Figure 4, this small variation in time means that the voltage falling across the contacts for a given range of regulation will vary from a very small negative voltage to a Very small positive Voltage. Furthermore, the magnitude of these voltages will be small enough to cause little eifect on Contact wear.

The operation of Figure 3 is almost exactly the same as the operation of the circuit of Figure l and is briefly as follows:

At time to the auxiliary voltage winding 23 initiates the by-pass circuit current through closing coil 26, diode 32, load 29 and back to the common point of Y -connected secondary 22. Upon reaching the magnitude of ampere turns required to close armature 50, the armature will close and current will be conducted through the main path, transformer 22, commutating reactor 28, contact 50 and load 29 after saturation of commutating reactor 28. Here again iiux reversal winding 33 controls the length of the make step thus controlling the output voltage.

The main difference between this circuit and the circuit of Figure l is that the control current now ows through load 29. Therefore, if the load impedance is so high as to limit current flow through the by-pass circuit to a magnitude too low to close armature 50, this very low current will still flow through load 29. However, when the load impedance is low enough to allow closure of armature 50, then the main contacts will operate in parallel to the bypass circuit. Therefore, this circuit allows variation or" load current from zero to rated load conditons.

Although we have disclosed our invention in connection with specific embodiments thereof, it will now become apparent to those skilled in the art that many variations ancl modifications may be made. We prefer to be limited, therefore, not by the specific disclosures herein but only by the appended claims.

We claim:

l. An electromagnetic rectfiier supplying a D. C. load from a three phase A. C. source comprising a main transformer, commutating reactors, electromagnetic switches and by-pass circuits; said main transformer having a three phase primary winding and a three phase secondary winding; said commutating reactors having a main winding and a flux reversal control winding; said electromagnetic switch having cooperating contacts, a closing winding, a holding winding and an opening means; said by-pass circuits comprising in series a diode, an auxiliary secondary winding of said main transformer and said closing coil; each of said auxiliary windings constructed to have their voltage phase shifted from the voltage of the corresponding main secondary winding; each phase of said electromagnetic rectiiier comprising in series one of said main transformer secondary windings, commutating reactor main windings, holding windings and electromagnetic switch cooperating contacts; each phase of said three phase transformer winding connected to deliver power to said D. C. load when said electromagnetic switch cooperating contacts are engaged; each main secondaiy winding of said main transformer connected in parallel with a by-pass circuit; said auxiliary secondary winding voltage and the impedance of said by-pass circuit constructed to energize said closing coil suiiiciently to close said cooperating contacts when the voltage across said cooperating contacts is zero, said auxiliary winding voltage to maintain current in said by-pass circuit until the voltage of said auxiliary secondary winding reverses.

2. An electromagnetic rectier supplying a D. C. load from a three phase A. C. source comprising a transformer, commutating reactors, electromagnetic switches and bypass circuits; said main transformer having a three phase secondary winding; said commutating reactors having a main winding and a ux reversal control winding; said electromagnetic switch having cooperating contacts, a closing winding, `a holding winding and an opening means; said by-pass circuits comprising in series a diode, an auxiliary winding of said transformer and said closing coil; each of said auxiliary windings constructed to have their voltage phase shifted from the voltage of the corresponding secondary winding; each phase of said electromagnetic rectifier comprising in series one of said transformer secondary windings, commutating reactor main windings, holding windings and electromagnetic switch cooperating contacts; each phase of said three phase secondary winding connected to deliver power to said D. C. load when said electromagnetic switch cooperating contacts are en gaged; each of said secondary windings connected in parallel with a by-pass circuit; said auxiliary winding voltage and the impedance of said by-pass circuit constructed to energize said closing coil suiciently to close said cooperating contacts when the voltage across said cooperating contacts is zero.

3. An electromagnetic rectiiier supplying a D. C. load from an A. C. source comprising a transformer, commutating reactors, electromagnetic switches and by-pass circuits; said main transformer having a secondary winding; said commutating reactors having a main winding and a iiux reversal control Winding; said electromagnetic switch having cooperating contacts, a closing winding, a holding winding and an opening means; said by-pass circuits comprising in series a diode, an auxiliary winding of said trans former and said closing coil; each of said auxiliary windings constructed to have their voltage phase shifted from the voltage of said secondary windings; said transformer secondary windings, commutating reactor main windings, holding windings and electromagnetic switch cooperating contacts connected in series with said D. C. load when said electromagnetic switch cooperating contacts are engaged; said secondary windings connected in parallel with said hy-pass circuit; said auxiliary winding voltage and the impedance of said by-pass circuit constructed to energize said closing coil sufficiently to close said cooperating contacts when the voltage across said cooperating contacts is zero.

4. An electromagnetic rectifier supplying a D. C. load from an A. C. source comprising a commutating reactor, electromagnetic switch and by-pass circuit; said electromagnetic switch having cooperating contacts, opening means, a main winding, and closing means; said by-pass circuit comprising in series a diode, an auxiliary voltage source and said closing means; said auxiliary voltage source constructed to have its voltage phase shifted from the voltage of said A. C. source; said A. C. source, cornmutating reactor, main winding and electromagnetic switch cooperating contacts connected in series to said D. C. load; said A. C. source in parallel with said by-pass circuit; said auxiliary voltage source and the impedance of said oy-pass circuit constructed to energize said closing means sufficiently to close said cooperating contacts when the voltage across said cooperating contacts is zero.

5. An electromagnetic rectifier supplying a D. C. load from a three phase A. C. source comprising a main transformer, commutating reactors, electromagnetic switches and by-pass circuits; said main transformer having a three phase primary winding and a three phase secondary winding; said commutating reactors having a main winding and a flux reversal control winding; said electromagnetic switch having cooperating contacts; a closing winding, a holding winding and an opening means; said by-pass circuits comprising in series a diode, an auxiliary secondary winding of said main transformer and said closing coil; each of said auxiliary windings constructed to have their voltage phase shifted from the voltage of the corresponding main secondary winding; each phase of said electromagnetic rectifier comprising in series one of said main transformer secondary windings, commutating reactor main windings, holding windings and electromagnetic switch cooperating contacts; each phase of said three phase transformer winding connected to deliver power to said D. C. load when said electromagnetic switch cooperating contacts are engaged; each series connection of said commutating reactor main winding, holding coil and electromagnetic switch cooperating contacts connected in parallel with a by-pass circuit; said auxiliary secondary winding voltage and the impedance of said by-pass circuit constructed to energize said closing coil suiiciently to close said cooperating contacts when the voltage across said cooperating contacts is zero, said auxiliary winding Voltage to maintain current in said by-pass circuit until the voltage of said auxiliary secondary winding reverses.

6. An electromagnetic rectifier supplying a D. C. load from a three phase A. C. source comprising a transformer, commutating reactors, electromagnetic switches and by-pass circuits; said main transformer having a three phase secondary winding; said commutating reactors having a main winding and a ux reversal control winding; said electromagnetic switch having cooperating contacts, a closing winding, a holding winding and an opening means; said by-pass circuits comprising in series a diode, an auxiliary winding of said transformer and said closing coil; each of said auxiliary windings constructed to have their voltage phase shifted from the voltage of the corresponding secondary winding; each phase of said electromagnetic rectifier comprising in series one of said transformer secondary windings, commutating reactor main windings, holding windings and electromagnetic switch cooperating contacts; each phase of said three phase secondary winding connected to deliver power to said D. C. load when said electromagnetic switch cooperating contacts are engaged; each series connection of said commutating reactor main winding, holding coil and electromagnetic switch cooperating contacts connected in parallel with a by-pass circuit; said auxiliary winding voltage and the impedance of said by-pass circuit constructed to energize said closing coil suiciently to close said cooperating contacts when the voltage across said cooperating contacts is zero.

7. An electromagnetic rectifier supplying a D. C. load from an A. C. source comprising a transformer, commutating reactors, electromagnetic switches and by-pass circuits, said main transformer having a secondary winding; said commutating reactors having a main Winding and a flux reversal control winding; said electromagnetic switch having cooperating contacts, a closing winding, a holding winding and an opening means; said by-pass circuits comprising in series a diode, an auxiliary winding of said transformer and said closing coil; each of said auxiliary windings constructed to have their voltage phase shifted from the voltage of said secondary winding; said transformer secondary windings, commutating -reactor main windings, holding windings and electromagnetic switch cooperating contacts connected in series with said D. C. load when said electromagnetic switch cooperating contacts are engaged; said by-pass circuit connected in parallel with said series connection of said commutating reactor main winding, holding winding and electromagnetic switch cooperating contacts; said auxiliary winding voltage and the impedance of said by-pass circuit constructed to energize said :closing coil suciently to close said cooperating contacts when the voltage across said cooperating contacts is zero.

8. An electromagnetic rectifier supplying a D. C. load from an A. C. source comprising a commutating reactor, electromagnetic switch and by-pass circuit; said electromagnetic switch having cooperating contacts, opening means, a main winding, and closing means; said by-pass circuit comprising in series a diode, an auxiliary voltage source and said closing means; said auxiliary voltage source constructed to vhave its voltage phase shifted from the voltage of said A. C. source; said A. C. source, commutating reactor, main winding and electromagnetic switch lcooperating contacts connected in series to said D. C. load; said series connection of said A. C. source and D. C. load connected in parallel to said by-pass circuit; said auxiliary voltage source and the impedance of said by-pass circuit constructed to energize said closing means suiciently to close said :cooperating contacts when the voltage across said cooperating contacts is zero.

References Cited in the file of this patent UNITED STATES PATENTS 2,617,974 Kesselring et al. Nov. 11, 1952 2,619,628 Kesselring Nov. 25, 1952 2.691,128 Weyener Oct. 5, 1954 FOREIGN PATENTS 113,439 Sweden Mar. 13, 1945 915,246 Germany July 19, 1954 

